Question: Which of these numbers is composite? ${11,\ 13,\ 23,\ 71,\ 86}$
A composite number is a number that has more than two factors (including 1 and itself). 11, 13, 23, and 71 each have only two factors. The factors of 86 are 1, 2, 43, and 86. Thus, 86 is the composite number.